Our work is directed towards the precise definition of the ribonucleoprotein structure of the mouse Beta globin major gene transcript and to the development of a meaningful assay for this structure. Regions of accessibility to exogenous nuclease have been identified by digestion of intact DMSO-induced Friend cell nuclei with Staphylococcal nuclease. The position of these areas in the transcript as regards the known sequence is currently being determined. Further, evidence has been obtained for a very well protected transcript related to the globin gene, and this too is being investigated.